1. Field of the Invention
The present invention relates to an improved method and device for igniting engines of automobiles and the like, and more particularly for igniting the engines by applying the same secondary high voltage polarity to all of the spark plugs under each of both compression and exhaust strokes in the case of the so-called simultaneous ignition system.
2. Description of the Prior Art
Recently, the high-powered engines for automobiles required for achieving accelerating ability and quick driving response as well as the greatest fuel economy has necessitated mounting a microcomputer with a sizeable memory in a car and controlling closely the ignition timing as well as the mixing ratio and quantity of air-fuel mixture according to actual driving conditions.
As regards the ignition device delivering an electric discharge by providing the spark plugs with a high voltage, the conventional ignition devices have often delivered the high voltage on the secondary side of the ignition coil after disconnecting a contact point of the distributor and have distributed such a high voltage to each cylinder through the distributor. Such devices have created problems such as damage to the above contact point or have been so unable to maintain their functions in a state of rapid rotation that it has been difficult for such devices to adapt to the above engine's performance. This is the reason why recently the above contact point has fallen out of use, and by the technique of generating the high voltage through turning transistors on and off, a large number of electronic ignition devices have been developed so far and put to practical use.
In addition, the above electronic ignition devices have further developed to include what is called the simultaneous ignition system which is currently employed in existing automobile engines.
FIG. 10 illustrates an example of an ignition device circuit with the above simultaneous ignition system. As shown in FIG. 10, among the spark plugs P1 to P6, a plug under compression stroke is combined with a plug under exhaust stroke (in the case of a six cylinder engine, for example, the 1st and 6th cylinders, 2nd and 5th cylinders, and 3rd and 4th cylinders might be paired) and they are connected to the sparking coils C1 to C3 from which both ends of the secondary coil are taken as the outputs. Once the transistors Q1 to Q3 connecting to the primary side of the above sparking coils C1 to C3 are turned on and off in sequence by trigger signals obtained through signals detected from the engine, the sparking coils will deliver a high voltage at the secondary side of the sparking coils. Thus such devices are arranged so that the plugs under compression strokes are ignited in sequence and, simultaneously, even the plugs under exhaust strokes are also ignited.
Even though it seems that the conventional ignition device's ignition under exhaust strokes is apparently useless, such devices have produced good effects in the prior art including prevention against a lower critical cooling rate for the spark plug and improvement in start-up as a result of improved control over idling rotation and torque variation. Nevertheless, significant offsetting negative effects have also been proven.
As shown distinctly in FIG. 10, a set of plugs P1 and P6 in a conventional ignition device is so connected to + and - sides of an ignition coil (C1) that such a device allows the spark plug set to experience lack of unity of polarity at discharge such that, for example, a spark plug P1 of the first cylinder always performs negative discharge, while the other one, P6 of the sixth cylinder, always performs positive discharge. Since the negative discharge is usually advantageous for the spark plug, the result is that the discharge efficiency in such spark plugs with positive discharge is lower than that of negative discharge, or their plugs are subject to serious damage. Furthermore, the engine, as a whole, not only has its balance made worse and the burning state of its spark plugs uneven due to their different discharge polarities, but also, as regards the spark plug, it will not be available to use with a timing light.